The study enrolled 31 patients between 2009 and 2014. Of 24 newly diagnosed patients, 17 had high-risk cytogenetics and 7 had high-risk disease on the basis of serum β2 microglobulin level > 5.5 g/dL. Seven patients were enrolled on the basis of relapsed disease after previous autologous HCT (n = 6) or induction treatment failure (n = 1); these patients had a median of three prior treatment regimens.

High-dose conditioning for autologous HCT consisted of melphalan at 200 mg/m2. Nonmyeloablative conditioning for allogeneic HCT involved low-dose total-body irradiation at 2 Gy with or without fludarabine at 30 mg/m2 for 3 days. Bortezomib maintenance was given at 1.6 mg/m2 intravenously or 2.6 mg/m2 subcutaneously every 14 days for 9 months.

Outcomes

Among the 31 patients, 26 (84%) received human leukocyte antigen (HLA)-matched allogeneic HCT at a median of 61 days (range = 41–168 days) after autologous HCT, and 21 patients (68%) started bortezomib maintenance at a median of 79 days (range = 63–103 days) after allogeneic HCT. On an intent-to-treat analysis at a median follow-up of 51 months (range = 16–86 months), 2- and 4-year progression-free survival rates were 71% and 52%, and 2- and 4-year overall survival rates were 75% and 61%, respectively, among the 24 newly diagnosed patients. Among the seven patients with relapsed/persistent disease, 2- and 4-year progression-free survival rates were 14% and 14%, and 2- and 4-year overall survival rates were 43% and 29%, respectively.

The investigators concluded: “These findings suggest that for patients with newly diagnosed high-risk multiple myeloma, bortezomib maintenance therapy after tandem autologous/allogeneic hematopoietic cell transplantation is safe and may prevent disease progression until full establishment of a graft-versus-myeloma effect. This benefit, however, does not extend to patients who enroll after unsuccessful prior therapy.”

The study was supported by the National Institutes of Health; the National Heart, Lung, and Blood Institute; and the National Cancer Institute as well as Millennium Pharmaceuticals, Inc/Takeda Oncology.